Combination 4 2025

In normal driving, some drivers use the hand valve before applying the brake pedal to prevent a jackknife. Which of these statements is true?

• It results in less skidding than using the brake pedal alone

• It is the best way to brake and keep the truck in a straight line

• It should not be done

You should not back a tractor under a trailer until the whole air system is:

• Half the maximum pressure

• Between 60 and 80 PSI

• At normal pressure

After you supply air to the trailer, make sure the airlines are not crossed and the trailer brakes are working. This can be done by:

• Turning on the parking brakes from the cab

• Lifting the brake pedal

• Applying and releasing the trailer brakes and listening for brake sounds

What is the safest way for you to make a turn without entering another traffic lane?

• If you must cross into the oncoming lane to make a turn and you see vehicles coming toward you, stop and back up for them.

• You should turn wide before you start the turn.

• You should turn wide as you complete the turn.

Even before antilock braking systems (ABS) were required, some vehicles already had them. How can you check if your vehicle has ABS?

• Look under the vehicle for the ABS test light.

• Brake the vehicle on a slippery road and see if the wheels lock.

• Look under the vehicle for the ECU and wheel speed sensor wires coming from the back of the brakes.

What is the emergency air line?

• Air lines that control the emergency brakes of the tractor

• Air lines connecting the parking brake to the trailer brakes

• Air lines that control the emergency brakes on combination vehicles

You are uncoupling a trailer. After you shut off the trailer air supply and lock the trailer brakes, you should

• begin to lower the trailer landing gear.

• immediately apply your tractor parking brakes.

• back up gently to ease pressure on the fifth wheel locking jaws.

A tractor with a(n) _______ trailer requires the shortest amount of stopping distance.

• empty

• lightly loaded

• fully loaded

The tractor protection valve will close and the trailer_______ brakes will come on when there is a major leak in the brake line.

• service

• parking

• emergency

You have a major leak in the service line, and you put on the brakes. Service air pressure will escape and cause the:

• Trailer tank pressure to be lost

• Tractor spring brakes to lock on

• Trailer emergency / spring brakes to come on